[PATCH] fix a NULL pointer dereference in amdgpu_connector_lcd_native_mode()

[PATCH] fix a NULL pointer dereference in amdgpu_connector_lcd_native_mode()

[Zhou Qingyang]

In amdgpu_connector_lcd_native_mode(), the return value of
drm_mode_duplicate() is assigned to mode, and there is a dereference
of it in amdgpu_connector_lcd_native_mode(), which will lead to a NULL
pointer dereference on failure of drm_mode_duplicate().

Fix this bug add a check of mode.

This bug was found by a static analyzer. The analysis employs
differential checking to identify inconsistent security operations
(e.g., checks or kfrees) between two code paths and confirms that the
inconsistent operations are not recovered in the current function or
the callers, so they constitute bugs.

Note that, as a bug found by static analysis, it can be a false
positive or hard to trigger. Multiple researchers have cross-reviewed
the bug.

Builds with CONFIG_DRM_AMDGPU=m show no new warnings, and
our static analyzer no longer warns about this code.

Fixes: d38ceaf99ed0 ("drm/amdgpu: add core driver (v4)")
Signed-off-by: Zhou Qingyang <zhou1615@umn.edu>
---
 drivers/gpu/drm/amd/amdgpu/amdgpu_connectors.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_connectors.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_connectors.c
index 0de66f59adb8..0170aa84c5e6 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_connectors.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_connectors.c
@@ -387,6 +387,9 @@ amdgpu_connector_lcd_native_mode(struct drm_encoder *encoder)
 	    native_mode->vdisplay != 0 &&
 	    native_mode->clock != 0) {
 		mode = drm_mode_duplicate(dev, native_mode);
+		if (!mode)
+			return NULL;
+
 		mode->type = DRM_MODE_TYPE_PREFERRED | DRM_MODE_TYPE_DRIVER;
 		drm_mode_set_name(mode);
 
-- 
2.25.1

Re: [PATCH] fix a NULL pointer dereference in amdgpu_connector_lcd_native_mode()

[Alex Deucher]

On Tue, Nov 30, 2021 at 6:24 AM Zhou Qingyang <zhou1615@umn.edu> wrote:
>
> In amdgpu_connector_lcd_native_mode(), the return value of
> drm_mode_duplicate() is assigned to mode, and there is a dereference
> of it in amdgpu_connector_lcd_native_mode(), which will lead to a NULL
> pointer dereference on failure of drm_mode_duplicate().
>
> Fix this bug add a check of mode.
>
> This bug was found by a static analyzer. The analysis employs
> differential checking to identify inconsistent security operations
> (e.g., checks or kfrees) between two code paths and confirms that the
> inconsistent operations are not recovered in the current function or
> the callers, so they constitute bugs.
>
> Note that, as a bug found by static analysis, it can be a false
> positive or hard to trigger. Multiple researchers have cross-reviewed
> the bug.
>
> Builds with CONFIG_DRM_AMDGPU=m show no new warnings, and
> our static analyzer no longer warns about this code.
>
> Fixes: d38ceaf99ed0 ("drm/amdgpu: add core driver (v4)")
> Signed-off-by: Zhou Qingyang <zhou1615@umn.edu>
> ---
>  drivers/gpu/drm/amd/amdgpu/amdgpu_connectors.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_connectors.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_connectors.c
> index 0de66f59adb8..0170aa84c5e6 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_connectors.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_connectors.c
> @@ -387,6 +387,9 @@ amdgpu_connector_lcd_native_mode(struct drm_encoder *encoder)
>             native_mode->vdisplay != 0 &&
>             native_mode->clock != 0) {
>                 mode = drm_mode_duplicate(dev, native_mode);
> +               if (!mode)
> +                       return NULL;
> +

The else if clause needs a similar check.  Care to fix that up as well?

Alex

>                 mode->type = DRM_MODE_TYPE_PREFERRED | DRM_MODE_TYPE_DRIVER;
>                 drm_mode_set_name(mode);
>
> --
> 2.25.1
>

[PATCH v2] drm/amdgpu: Fix a NULL pointer dereference in amdgpu_connector_lcd_native_mode()

[Zhou Qingyang]

In amdgpu_connector_lcd_native_mode(), the return value of
drm_mode_duplicate() is assigned to mode, and there is a dereference
of it in amdgpu_connector_lcd_native_mode(), which will lead to a NULL
pointer dereference on failure of drm_mode_duplicate().

Fix this bug add a check of mode.

This bug was found by a static analyzer. The analysis employs
differential checking to identify inconsistent security operations
(e.g., checks or kfrees) between two code paths and confirms that the
inconsistent operations are not recovered in the current function or
the callers, so they constitute bugs.

Note that, as a bug found by static analysis, it can be a false
positive or hard to trigger. Multiple researchers have cross-reviewed
the bug.

Builds with CONFIG_DRM_AMDGPU=m show no new warnings, and
our static analyzer no longer warns about this code.

Fixes: d38ceaf99ed0 ("drm/amdgpu: add core driver (v4)")
Signed-off-by: Zhou Qingyang <zhou1615@umn.edu>
---
Changes in v2:
  -  Fix the similar bug in else clause

 drivers/gpu/drm/amd/amdgpu/amdgpu_connectors.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_connectors.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_connectors.c
index 0de66f59adb8..df1f9b88a53f 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_connectors.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_connectors.c
@@ -387,6 +387,9 @@ amdgpu_connector_lcd_native_mode(struct drm_encoder *encoder)
 	    native_mode->vdisplay != 0 &&
 	    native_mode->clock != 0) {
 		mode = drm_mode_duplicate(dev, native_mode);
+		if (!mode)
+			return NULL;
+
 		mode->type = DRM_MODE_TYPE_PREFERRED | DRM_MODE_TYPE_DRIVER;
 		drm_mode_set_name(mode);
 
@@ -401,6 +404,9 @@ amdgpu_connector_lcd_native_mode(struct drm_encoder *encoder)
 		 * simpler.
 		 */
 		mode = drm_cvt_mode(dev, native_mode->hdisplay, native_mode->vdisplay, 60, true, false, false);
+		if (!mode)
+			return NULL;
+
 		mode->type = DRM_MODE_TYPE_PREFERRED | DRM_MODE_TYPE_DRIVER;
 		DRM_DEBUG_KMS("Adding cvt approximation of native panel mode %s\n", mode->name);
 	}
-- 
2.25.1

Re: [PATCH v2] drm/amdgpu: Fix a NULL pointer dereference in amdgpu_connector_lcd_native_mode()

[Alex Deucher]

Applied.  Thanks!

Alex

On Thu, Dec 2, 2021 at 11:17 AM Zhou Qingyang <zhou1615@umn.edu> wrote:
>
> In amdgpu_connector_lcd_native_mode(), the return value of
> drm_mode_duplicate() is assigned to mode, and there is a dereference
> of it in amdgpu_connector_lcd_native_mode(), which will lead to a NULL
> pointer dereference on failure of drm_mode_duplicate().
>
> Fix this bug add a check of mode.
>
> This bug was found by a static analyzer. The analysis employs
> differential checking to identify inconsistent security operations
> (e.g., checks or kfrees) between two code paths and confirms that the
> inconsistent operations are not recovered in the current function or
> the callers, so they constitute bugs.
>
> Note that, as a bug found by static analysis, it can be a false
> positive or hard to trigger. Multiple researchers have cross-reviewed
> the bug.
>
> Builds with CONFIG_DRM_AMDGPU=m show no new warnings, and
> our static analyzer no longer warns about this code.
>
> Fixes: d38ceaf99ed0 ("drm/amdgpu: add core driver (v4)")
> Signed-off-by: Zhou Qingyang <zhou1615@umn.edu>
> ---
> Changes in v2:
>   -  Fix the similar bug in else clause
>
>  drivers/gpu/drm/amd/amdgpu/amdgpu_connectors.c | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_connectors.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_connectors.c
> index 0de66f59adb8..df1f9b88a53f 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_connectors.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_connectors.c
> @@ -387,6 +387,9 @@ amdgpu_connector_lcd_native_mode(struct drm_encoder *encoder)
>             native_mode->vdisplay != 0 &&
>             native_mode->clock != 0) {
>                 mode = drm_mode_duplicate(dev, native_mode);
> +               if (!mode)
> +                       return NULL;
> +
>                 mode->type = DRM_MODE_TYPE_PREFERRED | DRM_MODE_TYPE_DRIVER;
>                 drm_mode_set_name(mode);
>
> @@ -401,6 +404,9 @@ amdgpu_connector_lcd_native_mode(struct drm_encoder *encoder)
>                  * simpler.
>                  */
>                 mode = drm_cvt_mode(dev, native_mode->hdisplay, native_mode->vdisplay, 60, true, false, false);
> +               if (!mode)
> +                       return NULL;
> +
>                 mode->type = DRM_MODE_TYPE_PREFERRED | DRM_MODE_TYPE_DRIVER;
>                 DRM_DEBUG_KMS("Adding cvt approximation of native panel mode %s\n", mode->name);
>         }
> --
> 2.25.1
>